http://www.linuxinsight.com/proc_sys_vm_hierarchy.html has some documentation on all the various bits in there, although I can't vouch for its readability for nongeeks. There's probably other important /proc docs there too, but I didn't look too far. I was just curious as to what "laptop mode" was, personally.

In the process, I did discover that "laptop_mode" is almost certainly useless. Roughly speaking, it cleans out old parts of the swap opportunistically any time any other I/O occurs - this saves power on a laptop because that way you avoid spinning up the hard drive *just* to handle swap cleanup. Last I checked, though, the n900 does not have a mechanical hard drive - unless someone's come up with a new mod I haven't heard about - and so this is unlikely to be helpful. (It's probably equally unlikely to be harmful, though, so, meh. )

I therefore suspect some of the other tweaks listed may arise from a similar "shotgun approach" to tweak application, but I haven't looked all that closely.